Grid construction



y 1936- I J. H. CONE 2,041,904

GRID CONSTRUCTION Filed April 4, 1931 INVENTOR JAMES H. (O/V5.

ATT RNEY Patented May 26, 1936 1 UNITED STATES PATENT OFFICE GRIDCONSTRUCTION James H. Cone, Roseland, N. J., assignor to National UnionRadio Corporation, Newark, N. J a corporation of Delaware This inventionrelates to a grid construction, more particularly that of the controlgrid, of a vacuum tube. r

It is known to those skilled in the art that problems in distortion andcross-talk occasioned in tubes used in the radio frequency stages of areceiving set, are manifested in self-rectification produced in thetube. A simple explanation of these problems is that they are caused bya sudden change in the plate current, with a consequent change in themutual conductance of the tube. Since the accepted definition of mutualconductance is the slope of the plate current curve, a sudden change inthe slope thereof will cause distortion or cross-talk.

In an attempt to overcome these difficulties, tubes with exponentialcharacteristics have been designed, as for example reference may be madeto an article by Ballatine and Snow, published in the December 1930issue (vol. 18, No. 12) of Proceedings of The Institute of RadioEngineers, pages 2102-27.

It has been discovered that the true exponential characteristics of a.tube can be expressed by a formula which would give a true exponentialcurve.

It is an object of my invention to provide a grid construction havingthe turns thereof spaced, so that the plate current and mutualconductance of a tube embodying the same will follow approximately atrue exponential curve.

Another object is to provide such a control grid of which the turnsthereof are symmetrical.

A further object is the provision of a grid construction, having extremesimplicity yet adapted to produce a tube with exponentialcharacteristics.

Other objects of the invention will manifest themselves as thedescription proceeds.

In accordance with my invention there is provided a grid, the turns ofwhich are symmetrically arranged and spaced according to my formula.When a grid conforming to this construction is mounted in the vacuumtube it will produce characteristics which will conform substantially toa true exponential curve.

In the accompanying drawing:

Fig. 1 schematically represents an enlarged '50 plan view of a controlgrid embodying the invention;

Fig. 2 is an end view of the grid shown in Fig. 1;

Fig. 3 is a sectional view diagrammatically illustrating the arrangementof the cathode, grid,

and plate of a three element tube embodying the invention;

Fig. 4 is a view similar to Fig. 3 illustrating the invention as appliedto a tetrode type tube; and

Fig. 5 is a graph showing true exponential curves of plate current andmutual conductance obtained by using a grid having the constructionshown in Fig. 1.

It has been discovered by prior workers of the art that a trueexponential'curve may be expressed by the following formula:

Where a and K are constants for a given construction. e the base ofnatural logarithms. Eg the value of the applied control grid voltage.

plotted against applied grid voltages. I developed such a formula forthe space between turns, said formula taking the following generalK1=space between wire for first turn.

K2=empirical constant.

N =number of turns from end of grid.

=constant exponent.

The term exponential when used in relation to'the grid spacing of agiven tube is not mathematically correct, since the exponent a. becomesa constant for any given grid. However, from the standpoints of grids ingeneral, my equation is exponential since "a is a variable.

This will give us a grid with the wires widely spaced at one end andclosely spaced at the other. It is evident that the grid should besymmetrical; therefore, both halves of the active grid length should becomplementary to each other, sothat a complete grid starting with thecenter turn would have each adjacent turn on one side complementary to acorresponding adjacent turn on the other side.

In applying the form of grid shown in Fig. 1 was designed. As is commonpractice in the construction of control grids, the wire I is spirallywound about a pair of support wires 2, separated at their ends by acylindrical spacing element 3 provided with apertures 4, through whichthe ends of the support wires extend. The respective turns of the gridwire may be welded to the support wires, or fastened in any otherapproved manner. The spacing of the turns, derived from the are asfollows:

s=wire spacing 1st 11 turns s=.0120 12th turn s=.0124 13th turn s==.015614th turn s=.0242 15th turn s=.0410 16th turn s=.0690

17th turn s=.1100 18th turn s=.1100 19th turn s ..0690 20th turn 8:.0410

21st turn s=.0242 22nd turn s: 0156 23rd turn 0124 Last 11 turns s=.0120

Total turns 34 Grid length .813"

The grid wire diameter, grid diameter and plate or anode distance togrid will not affect the shape of the curve but will shift the curvewith respect to the coordinates, nor will a change in cathode or anodearea change the shape of the curve, as shown by the constant 13 above.

Referring to Figs. 3 and 4 the tube elements are diagrammaticallyillustrated and show the invention applied to a three element and a fourelement type tube, respectively. The filament II] is enclosed within acathode sleeve II, and adjacent to the cathode is placed the grid I 2,having the turns thereof variably spaced in accordance with my formula.In Fig; 3 the plate is designated by the reference character l3, whilein Fig. 4 it is identified as I5. The shield, and shield grid, beingelectrically connected, are designated by the single reference l4. Asthe function of these elements is well understood in the art, there isno occasion to show any circuit arrangements, nor further detail ofconstruction.

From the foregoing description it is obvious that the advantage of atube embodying the invention will have greatly reduced rectificationfrom the standpoint that whatever rectification takes place it will bemore or less uniformly distributed or spread along the exponentialcurve, and in that manner distributed so as to be practicallyunnoticeable during the functioning of the tube.

It is not intended to be limited by the exact disclosure set forth asvariations and substitutions may be made within the range or limitsdefined by the claims. For example, it may be found advantageous toreverse the spacing of the turns of the grid so that the central turnhas a small pitch which becomes increasingly coarser toward the ends.Furthermore, for various reasons it may be desirable to make the gridflat instead of cylindrical in shape. All such modifications arecontemplated by me as come within the scope of the claims.

where K1=space between wire for first turn Kz=empirical constantN=number of turns from end of grid a constant exponent said spacinggiving the tube a mutual conductance-grid bias curve which ispractically a straight line when plotted on semi-log paper.

2. An electron discharge device comprising an anode, an emitter, aplurality of grids surrounding the emitter within the anode, the spacingn of the turns of one of said grids being in accordance with the formulahaving the following general form:

N a 11 1+ K2 E where K1=space between wire for first turn Kz=empiricalconstant N=number of turns from end of grid a constant exponent saidspacing giving the tube a mutual conductance-grid bias curve which ispractically a straight line when plotted on semi-10g paper.

3. A grid construction comprising a grid having a wider mesh at thecentral portion than at the ends, the meshes of the two halves of saidgrid being complementary with respect to the central portion thereof andthe spacing n of the turns of each half being determined by thefollowing formula:

where K1=space between wire for first turn Kz=empirical constant =numberof turns from end of grid a=constant exponent 4. A grid constructioncomprising a grid continuously wound and having the form of a completeenclosing circuit, the turns of said grid being symmetrically arrangedand uniform in diameter from end to end, the spacing n of the turns ofsaid grid being in accordance with the following formula:

where V K1=space between wire for first turn K2=empirical constantN=number of turns from end of grid a=constant exponent 5. An electrondischarge device comprising an anode, an emitter and a grid surroundingthe emitter within the anode, said grid being a conwhere K1=spacebetween wire for first turn K2=empirical constant N =number of turnsfrom end of grid a=constant exponent 6. An electron discharge devicecomprising an anode, an emitter and a grid surrounding the emitterwithin the anode, said grid being a control grid cylindrically shapedand having the turns thereof symmetrically arranged and uniform indiameter from end to end, the spacing n of the turns of said grid. beingin accordance with the formula having the following general form:

where K1=space between wire for first turn K2=empirical constantN=number of turns from end of grid a=constant exponent 7. An electrondischarge device comprising an anode, an emitter and a grid surroundingthe emitter within the anode, the spacing n of the turns of said gridbeing in accordance with the formula having the following general form:

Where K1=space between wire for first turn Kz=empirical constantN=number of turns from end of grid a=constant exponent JAMES H. CONE.

